The invention relates to a master cylinder, especially for a controlled brake system, comprising at least one piston displaceable in a housing, which is sealed in relation to a pressure chamber by means of a sealing element arranged in an annular groove of the housing, said pressure chamber being connectable to an unpressurized supply chamber by means of transverse bores provided in the piston.
A master cylinder of this type is e.g. disclosed in DE 101 20 913 A1, and the transverse bores therein have a small cross-section in order to keep the lost travel of the master cylinder as short as possible. When used in a controlled brake system such as a brake system with traction slip control (TSC) or an Electronic Stability Program (ESP), a pump will replenish pressure fluid from a pressure fluid tank through the master cylinder in the case of control intervention. It is disadvantageous in the arrangement that the small cross-section of the transverse bores produces an excessive throttling resistance and the required pressure fluid of the pump cannot be provided at a sufficiently quick rate.
EP 0 807 042 A1 discloses designing the transverse bores as slots which extend in a circumferential direction of the piston. As an outside surface of the piston (peripheral surface) is used to guide the piston, it is necessary to debur the slots on the outside surface of the piston. To this end, suggestions have been made to arrange the slots in the bottom of a circumferential outside groove, necessitating also the circumferential outside groove to be machined in order to prevent sharp edges and damage to the sealing element. It is also disadvantageous that an inside sealing lip of the sealing element, when overriding the circumferential outside groove, is urged by a preload into the outside groove, which can also cause damage or torsion of the inside sealing lip.
In view of the above, an object of the invention is to provide a master cylinder, which is improved in this respect.